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Comminution

Reduction Ratio Calculator

The comminution reduction ratio is how many times coarser the feed is than the product: R = F80 / P80, with both sizes in the SAME unit. From the feed size (F80) and product size (P80) this calculator returns the reduction ratio and the percent size reduction. It is a preliminary, formula-based, educational same-unit size ratio. It is NOT a particle-size conversion calculator (it does not convert mesh ↔ micron), NOT a crusher selection tool, and NOT a mill design tool, and it does not calculate energy, Bond Work Index, liberation, throughput, or equipment capacity. Final comminution design requires testwork, particle-size distributions, equipment data, and qualified review.

TypeInteractive engineering calculator

Calculator

µm

80% passing size of the feed

µm

80% passing size of the product (same unit as F80)

cosmetic only — F80 and P80 must already be in the same unit; the ratio is dimensionless

Result
Reduction ratio (F80 / P80)18.8679 : 1
Percent size reduction94.7 %
  • !Same-unit size ratio only — enter the feed size (F80) and product size (P80) in the SAME unit. This calculator does NOT convert particle sizes (e.g. mesh ↔ micron).
  • !It is not a crusher selection or mill design tool and does not calculate energy, Bond Work Index, liberation, throughput, or equipment capacity. Final comminution design requires testwork, PSDs, equipment data, and qualified review.

Preliminary, formula-based same-unit size ratio from user-supplied sizes. Not a particle-size conversion calculator, not a crusher selection tool, and not a mill design tool. Final comminution design requires testwork, particle-size distributions, equipment data, and qualified review.

Related: Grinding Circuit Calculations · Bond Work Index · Bond Work Index Explained · Circulating Load

Formulas

Reduction ratio
R = F80 / P80
Percent size reduction
% = (1 − P80 / F80) × 100

Diagram

Reduction ratio — F80 over P80, a same-unit size ratioF80coarse feedcomminutionP80fine productR = F80 / P80 (same unit)% reduction = (1 − P80/F80)·100a size ratio — not a crusher/mill selection or energy tool

Worked example

A grinding stage reduces a feed of F80 = 2000 µm to a product of P80 = 106 µm. Find the reduction ratio and percent size reduction.

  1. 01Reduction ratio: R = 2000 / 106 = 18.87
  2. 02Percent size reduction: (1 − 106 / 2000) × 100 = 94.7%
Result

Reduction ratio 18.87 with a 94.7% size reduction — a dimensionless same-unit size ratio, not an equipment-selection or energy result.

FAQ

What is the reduction ratio?
It is the feed size divided by the product size, R = F80 / P80 — a dimensionless number quantifying how much size reduction a comminution stage achieved. An R of 18.87 means the product 80%-passing size is about 1/19 of the feed 80%-passing size.
Do F80 and P80 have to be in the same unit?
Yes. The reduction ratio is a ratio of two sizes, so both must be in the same unit (both µm or both mm). This calculator does not convert between size units — entering mixed units (e.g. mesh and micron) would give a meaningless result. The unit label shown is cosmetic only.
Does the reduction ratio tell me which crusher or mill to use?
No. It quantifies size reduction but carries no energy, work index, throughput, or capacity information, so it cannot select or size equipment. Equipment selection needs testwork, vendor data, and qualified engineering review.
How does percent size reduction relate to the ratio?
Percent size reduction = (1 − P80/F80) × 100. It expresses the same reduction as a fraction of the feed size removed. A large reduction ratio corresponds to a percent size reduction approaching 100%; for example R = 18.87 is a 94.7% reduction.

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